A ghost is the form that all people and animals must take when dead. The person recently deceased must wait a year and a day in the place of their death before he or she can fully enter ghosthood. Ghosts can choose to Appear to the Living if they desire and they have no substance and thus will pass through objects. Ghosthood also has its laws that all ghosts must follow. A ghost may also be a haunting spirit such as a Spectre or a Shadow. There is place in The Castle called the Hole in the Wall Tavern where many ghosts (and generally only ghosts, with only a few exceptions) are welcome and a Living guest must be invited by at least two ghosts.
These are some abilities or actions that are commonly but not all exclusively possessed or done by ghosts.
- Spirits may choose to be seen by particular people if they desire. A Spirit-Seer can see ghosts even if they do not Appear.
- Ghosts can Cause objects to do certain things such as the slamming of doors or switching of socks. Alther Causes several things in the Wizard Tower in an attempt to annoy DomDaniel. Wizards may also Cause things to happen.
- Certain ghosts, especially Spectres and other haunting spirits, can Take the Living with them into ghosthood. It is possible to Take a Living person in the objective of simply transporting them to another place.
- Ghosts can be Passed Through by the Living. And person can simply walk through a ghost and this would leave the spirit feeling sick as if they had just ingested what went through them. This is the highest point of rudeness (if the ghost is visible) a Living Person may inflict upon a spirit.
- "A ghost may trod once more where, Living, he has trod before." One of the prime laws of ghosthood is that a ghost may only travel where he been before while he was alive. A ghost who tries to enter a place that he has not in Life will be violently Returned to his initial place. The experience is described to leave the spirit winded and out of breath. This causes some difficulty to the ghosts of the Castle as the structures are sometimes changed or modified, leaving the ghosts trapped. All ghosts are welcome in the Hole in the Wall Tavern and will not be Returned from it. Furthermore, a ghost may ride in a boat they have ridden in before to locations where they have not previously traveled. They will, however, be Returned, should they attempt to exit from the boat to a location they have not previously visited.
- Unlike Wizards who have long since lost the Art of Flyte, ghosts can freely and easily Flye.
- Ghosts can pass through solid objects by Discomposing themselves. Seems to be the same thing as Passing Through.
- After being Discomposed, ghosts can Rearrange themselves once they have passed through the object.
- A person who has recently died must Wait in the place of his or her death for a year and a day before he or she can fully enter ghosthood. A Spectre can be convinced to Wait by the person he plans to Take before he can be Taken, giving the person enough time to get rid of the Spectre.
- A ghost can Reclaime a person who is in desperate danger and is in a life or death situation. However, a Reclaime can be undone in the next twenty-four hours if the ghost wills it, putting that person back in his place of danger. Queen Etheldredda Reclaimes a drowning Septimus (even though she was the one who pushed him in the first place) and uses this to blackmail him and Jenna to do her bidding.
- Alther Mella: Jenna does not think he is really a Palace ghost, but insists on mentioning him. He is like a "ghost-grandfather" to her,
- Sir Hereward: Sir Hereward is Jenna's second favourite ghost, being the one who gaurds her room. He is said to only have one arm, and constantly tells the same joke over and over again, but is caring and protective of Jenna,
- Gudrun the Great: Gudrun is an ancient ghost who lives at the Palace Gate. She is very faded and cannot be seen in the sunlight.
- Godric: Godric used to gaurd the Palace door, but now sleeps in an armchair in the hall. It is noted that he sometimes snores.
- Fara Field: This is not her real name, but Jenna's nickname for her, as Fara says she can see danger coming from "farafield." She was formerly a housekeeper, but now wanders the battlements in an old uniform carrying a small piglet under her arm.
- Young Wainwright: He is a boy groom. Jenna often sees him asleep in the stable. Her horse, Domino, likes him, but she thinks he is strange as he tries to help brush her horse.
- The Unknown Princess: Seen only at full moons, she is crazy. She swims in the ornamental pool and waves her arms "like a jellyfish."
- Sir Bretticus-Petticus: Bretticus-Petticus was a knight and a Wizard, and also married a Queen. He is described as being "very rude" and told Jenna she did not look like "a real Princess." He was killed by his own Unstable spell of his own creation. He now walks the Long Walk with his feet on fire.
- Mary: A former governess to Princess Esmeralda's baby sisters, Mary is convinced that Jenna is the Esmeralda is always telling her to be careful. Jenna feels sorry for her, but stays clear if she sees the ghost coming.
- See the List of Queens
- Aie-Aie: A rat-like creature with a snake's tail. Pet of Queen Etheldredda and a bite of the Aie-Aie contains the Sickenesse.
- Namby-Pamby Mither of Mischief (not his real name):
- John: A Palace Guard who found Jenna and brought her to Queen Etheldredda. Later sent to the dungeons.
- Will: A Palace Guard who found Jenna and brought her to the Queen. Later sent to the dungeons.
- The Knight of the Day: Tried to capture Jenna Heap for the Queen.
- Stewer of Meates: Wife of either Will or John.
- Keeper of the Gravie Boate: Wife of either Will or John..
- The Bumptious Barrelle of Larde (given name Aloysius Umbrella! Tyresius Dupont): The Queen's Steward. Has ten gold ribbons. The Knight of the Day called him Percy.
- Broda Pye: Wife of Marcellus Pye. Spent time in the Queen's Potions Cupboard.
- Hugo Tenderfoot: Apprentice to Marcellus Pye and learned many things about Physik. Inspired by Septimus Heap.
- Olaf Snorrelssen: Father of Snorri. A sailor who died when he hit his head on the parapet of the One-Way Bridge.
- Sister Bernadette: A nun who spends her time at the Hole in the Wall Tavern.
- Hildeguard: One of the guards at the Castle.
- Endor: Marcia's Deputy. Killed by DomDaniel when trying to stop him.
- Alice Nettles (given name Iona Pot): Chief Customs Officer of the Port before death. Before that she was a judge. Shot by a named bullet.